1. Field of the Invention
The present invention relates to a congestion control method, a base station control unit and a mobile terminal in a mobile communication network.
2. Description of the Prior Art
Recently, mobile communications using mobile phones (including PHS phones) have become commonplace. A mobile communication network is made up of mobile terminals, wireless base stations, base station control units, exchanges and the like.
As a mobile communication becomes widespread, its traffic increases. If large quantity of calls and receptions are performed with mobile phones or the like in cases where a disaster occurred or an event is held, probability that a specific area will fall into a congestion state may be increased. If a congestion state occurs, calls and receptions as well as e-mail transmission and reception with mobile phones become impossible in the area. In addition, if the congestion state lasts long, the entire system of the mobile communication network will become unstable. In order to avoid such a situation, communications with mobile phones and the like in the area will be restricted if a congestion state occurs, so that the mobile communication network can be stabilized. In this case, with respect to emergency calls and high priority calls, communications or talking can be secured by using emergency wireless resources.
However, an ordinary user who cannot enjoy such a special treatment cannot make communication when a congestion state occurred. There is a case, however, where an ordinary user must make an urgent communication for an important matter. Nonetheless, an ordinary user is in such a state that he or she has just to wait until the congestion state of the mobile communication network will be relieved.
As a congestion control method in a mobile communication network, Japanese unexamined patent publication No. 5-292012 discloses a following method. A network side informs a mobile terminal side of a communication channel use ratio of each base station and a threshold of the use ratio. The mobile terminal side receives the information and determines whether or not a congestion state occurred. If it determines that a congestion state occurred, it requests a hand over in the case where a neighboring wireless communication zone has no problem in its communication quality.
In addition, Japanese unexamined patent publication No. 11-275646 discloses a following method. When the number of times of completing registration of location from a base station becomes a predetermined number or more, a network side distributes the traffic to a neighboring base station if there is not a problem in electric field level and communication channel use rate of the neighboring base station.
However, the above-mentioned method described in Japanese unexamined patent publication No. 5-292012 is a technique dealing with a state after a mobile phone or the like established communication so that the user can communicate with it, and it cannot resolve a trouble in the case where the user cannot communicate due to occurrence of the congestion state.
In addition, the method disclosed in Japanese unexamined patent publication No. 11-275646 is premised on that the registration of location is requested by the mobile phone. However, if a congestion state occurs, it is unable even to request the registration of location. Therefore, it also cannot resolve a trouble in the case where the user cannot communicate due to occurrence of the congestion state.
In addition, there is provided a technique of restricting communications with mobile phones in the area for relieving the congestion state of the network if the mobile communication network is congested, so as to secure network resources for emergency calls or high priority calls.
However, even if this technique is used, an ordinary user has just to wait until the congestion state will be relieved as described above.
In this way, one of the conventional proposed techniques is for avoiding occurrence of a congestion state and the other is for restricting communication when a congestion state occurred. But, they cannot cancel the congestion state promptly when it occurred.